899 research outputs found

    Regular Rooted Graph Grammars

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    In dieser Arbeit wir ein pragmatischer Ansatz zur Typisierung, statischen Analyse und Optimierung von Web-Anfragespachen, speziell Xcerpt, untersucht. Pragmatisch ist der Ansatz in dem Sinne, dass dem Benutzer keinerlei Einschränkungen aus Entscheidbarkeits- oder Effizienzgründen auf modellierbare Typen gestellt werden. Effizienz und Entscheidbarkeit werden stattdessen, falls nötig, durch Vergröberungen bei der Typprüfung erkauft. Eine Typsprache zur Typisierung von Graph-strukturierten Daten im Web wird eingeführt. Modellierbare Graphen sind so genannte gewurzelte Graphen, welche aus einem Spannbaum und Querreferenzen aufgebaut sind. Die Typsprache basiert auf reguläre Baum Grammatiken, welche um typisierte Referenzen erweitert wurde. Neben wie im Web mit XML üblichen geordneten strukturierten Daten, sind auch ungeordnete Daten, wie etwa in Xcerpt oder RDF üblich, modellierbar. Der dazu verwendete Ansatz---ungeordnete Interpretation Regulärer Ausdrücke---ist neu. Eine operationale Semantik für geordnete wie ungeordnete Typen wird auf Basis spezialisierter Baumautomaten und sog. Counting Constraints (welche wiederum auf presburgerarithmetische Ausdrücke) basieren. Es wird ferner statische Typ-Prüfung und -Inferenz von Xcerpt Anfrage- und Konstrukttermen, wie auch Optimierung von Xcerpt Anfragen auf Basis von Typinformation eingeführt.This thesis investigates a pragmatic approach to typing, static analysis and static optimization of Web query languages, in special the Web query language Xcerpt. The approach is pragmatic in the sense, that no restriction on the types are made for decidability or efficiency reasons, instead precision is given up if necessary. Pragmatics on the dynamic side means to use types not only to ensure validity of objects operating on, but also influencing query selection based on types. A typing language for typing of graph structured data on the Web is introduced. The Graphs in mind are based on spanning trees with references, the typing languages is based on regular tree grammars with typed reference extensions. Beside ordered data in the spirit of XML, unordered data (i.e. in the spirit of the Xcerpt data model or RDF) can be modelled using regular expressions under unordered interpretation – this approach is new. An operational semantics for ordered and unordered types is given based on specialized regular tree automata and counting constraints (them again based on Presburger arithmetic formulae). Static type checking of Xcerpt query and construct terms is introduced, as well as optimization of Xcerpt query terms based on schema information

    A Researcher’s Digest of GQL

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    International audienceGQL (Graph Query Language) is being developed as a new ISO standard for graph query languages to play the same role for graph databases as SQL plays for relational. In parallel, an extension of SQL for querying property graphs, SQL/PGQ, is added to the SQL standard; it shares the graph pattern matching functionality with GQL. Both standards (not yet published) are hard-to-understand specifications of hundreds of pages. The goal of this paper is to present a digest of the language that is easy for the research community to understand, and thus to initiate research on these future standards for querying graphs. The paper concentrates on pattern matching features shared by GQL and SQL/PGQ, as well as querying facilities of GQL

    Doctor of Philosophy

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    dissertationToday's smartphones house private and confidential data ubiquitously. Mobile apps running on the devices can leak sensitive information by accident or intentionally. To understand application behaviors before running a program, we need to statically analyze it, tracking what data are accessed, where sensitive data ow, and what operations are performed with the data. However, automated identification of malicious behaviors in Android apps is challenging: First, there is a primary challenge in analyzing object-oriented programs precisely, soundly and efficiently, especially in the presence of exceptions. Second, there is an Android-specific challenge|asynchronous execution of multiple entry points. Third, the maliciousness of any given behavior is application-dependent and subject to human judgment. In this work, I develop a generic, highly precise static analysis of object-oriented code with multiple entry points, on which I construct an eective malware identification system with a human in the loop. Specically, I develop a new analysis-pushdown exception-ow analysis, to generalize the analysis of normal control flows and exceptional flows in object-oriented programs. To rene points-to information, I generalize abstract garbage collection to object-oriented programs and enhance it with liveness analysis for even better precision. To tackle Android-specic challenges, I develop multientry point saturation to approximate the eect of arbitrary asynchronous events. To apply the analysis techniques to security, I develop a static taint- ow analysis to track and propagate tainted sensitive data in the push-down exception-flow framework. To accelerate the speed of static analysis, I develop a compact and ecient encoding scheme, called G odel hashes, and integrate it into the analysis framework. All the techniques are realized and evaluated in a system, named AnaDroid. AnaDroid is designed with a human in the loop to specify analysis conguration, properties of interest and then to make the nal judgment and identify where the maliciousness is, based on analysis results. The analysis results include control- ow graphs highlighting suspiciousness, permission and risk-ranking reports. The experiments show that AnaDroid can lead to precise and fast identication of common classes of Android malware

    Configuration spaces of disks in a strip, twisted algebras, persistence, and other stories

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    We give Z\mathbb{Z}-bases for the homology and cohomology of the configuration space config(n,w)\operatorname{config}(n,w) of nn unit disks in an infinite strip of width ww, first studied by Alpert, Kahle and MacPherson. We also study the way these spaces evolve both as nn increases (using the framework of representation stability) and as ww increases (using the framework of persistent homology). Finally, we include some results about the cup product in the cohomology and about the configuration space of unordered disks.Comment: 45 pages, 15 figures. Builds on and supersedes arXiv:2006.0124

    Eliminating Higher-Multiplicity Intersections, II. The Deleted Product Criterion in the rr-Metastable Range

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    Motivated by Tverberg-type problems in topological combinatorics and by classical results about embeddings (maps without double points), we study the question whether a finite simplicial complex K can be mapped into R^d without higher-multiplicity intersections. We focus on conditions for the existence of almost r-embeddings, i.e., maps from K to R^d without r-intersection points among any set of r pairwise disjoint simplices of K. Generalizing the classical Haefliger-Weber embeddability criterion, we show that a well-known necessary deleted product condition for the existence of almost r-embeddings is sufficient in a suitable r-metastable range of dimensions (r d > (r+1) dim K +2). This significantly extends one of the main results of our previous paper (which treated the special case where d=rk and dim K=(r-1)k, for some k> 3).Comment: 35 pages, 10 figures (v2: reference for the algorithmic aspects updated & appendix on Block Bundles added
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